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Fastly

Fastly is a commercial CDN + edge-compute platform, historically Varnish-based with VCL as the configuration language; widely used as the origin-fronting cache for high-profile sites. Distinctive trade-off: instant purges (seconds) + programmable edge via VCL and, more recently, Compute@Edge (WASM).

Wiki canonical instance

GitHub Pages puts Fastly in front of its nginx routing tier. The load-bearing architectural property: "We also have Fastly sitting in front of GitHub Pages caching all 200 responses. This helps minimise the availability impact of a total Pages router outage. Even in this worst case scenario, cached Pages sites are still online and unaffected." (Source: sources/2025-09-02-github-rearchitecting-github-pages)

Canonical instance of patterns/caching-proxy-tier: the CDN is used not primarily as a latency / bandwidth optimisation, but as the outage-survivability boundary. If the origin MySQL-backed routing layer goes down, the Fastly cache continues serving previously-200 sites. Freshly-published sites + non-200 paths are not covered — the property is definitionally about the cache-hit set.

Use-shape

  • 200-only caching — GitHub Pages' disclosed policy. Non-200 is passed through, which means the availability-fallback property doesn't extend to redirects, 404s, or origin errors. Trade-off is deliberate: non-200s often carry state that you don't want a CDN to replay.
  • CDN as load-shedder + availability layer — even in the common case, the cache absorbs >99% of hits for popular Pages sites.

Stub page

Stub anchoring Fastly's role in the wiki's first DB-routed static- hosting source. Broader Fastly coverage (VCL internals, Compute@Edge, instant-purge mechanic, private network, peering, per-POP architecture, Fastly vs Cloudflare design comparisons) out of scope.

Seen in

  • sources/2025-09-02-github-rearchitecting-github-pages — Fastly caches all 200 responses from GitHub Pages; during a total router outage cached Pages sites stay online — canonical instance of CDN-fronted availability fallback.
  • sources/2026-10-02-cloudflare-2026-birthday-week-network-performance-update — one of the five providers in Cloudflare's comparative RUM connection-time benchmark, and the named close-race example: Cloudflare cites "Cloudflare at 50 ms and Fastly at 51 ms" as a gap small enough that day-to-day noise can flip the ranking — the motivating case for expanding measurement volume (via Turnstile Challenge Pages) to narrow the confidence interval.
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